This invention relates to a circumferential flow type fuel pump for use in, e.g., combustion engines of motor vehicles having a centrifugal liquid pump.
FIG. 2 is a sectional view showing a conventional circumferential flow type fuel pump for a motor vehicle disclosed in, e.g., Japanese Patent Unexamined Publication No. 79193/1985 and FIG. 3 is a sectional view taken along line III--III of FIG. 2.
In FIGS. 2 and 3, a pump body 1 includes a power supply section 2, a motor 3, a centrifugal pump section 4, and an outer casing 5. A rotating shaft 3a of the motor 3 is pivotably supported by a first bearing 2a of the power supply section 2 and a second bearing 4a of the pump section 4.
The pump section 4 includes a pump casing 41, an impeller 42, and a pump cover 43. The pump casing 41 is press-fit into the outer casing 5. The pump cover 43 is secured to the open end portion of the outer casing 5 by caulking. The impeller 42 is disposed between the pump casing 41 and the pump cover 43. The impeller 42 has a substantially D-shaped hole 42b, and the center Q of the circular portion of this hole 42b coincides with the center P of the impeller 42. An end portion of the rotating shaft 3a fits into this hole 42b. The end portion of the rotating shaft 3a is substantially D-shaped like the hole 42b, with its diameter being slightly smaller than that of the hole 42b.
A circumferential fuel flow path 44 is formed in both the pump casing 41 and the pump cover 43 around the outer periphery of the impeller 42. Around the outer periphery of the impeller 42 facing the fuel flow path 44 are a plurality of vanes 42a which perform a pumping action.
An upstream end of the fuel flow path 44 communicates with a fuel inlet 45 disposed on the pump cover 43, while a downstream end of the fuel path 44 communicates with a delivery guide section 21 disposed at the power supply section 2 through an outlet 46 disposed at the pump casing 41 and a motor chamber. The upstream end and downstream end of the fuel flow path 44 neighbor through a flow path partition wall 41a disposed at the pump casing 41. The flow path partition wall 41a confronts the outer periphery of the impeller 42 with a tiny gap 6 therebetween.
The operation of the pump will be described next. The motor 3 is driven by an external power source through the power supply section 2. The motor 3 causes the impeller 42 engaged with the rotating shaft 3a of the motor to rotate, thereby making the impeller serve as a pump and sucking fuel from the inlet 45. The sucked fuel flows from the fuel flow path 44 to the outlet 46, the motor chamber, and to the delivery guide section 21 so as to be supplied to an engine (not shown).
Most of the fuel that flows to the downstream end of the fuel flow path 44 collides with the flow path partition wall 41a and flows into the outlet 46. However, part of this fuel returns to the upstream end of the fuel flow path 44 through the tiny gap 6.
As shown in FIG. 3, when the impeller 42 is rotated clockwise in the figure, the center O of the portion which is circular in section of the rotating shaft 3a coincides with the center P of the impeller 42 and is deviated by substantially half the difference in diameter between the rotating shaft 3a and the hole 42b, i.e., .DELTA.r, since both the end portion of the rotating shaft 3a and the hole 42b are substantially D-shaped and, at the same time, the end portion of the rotating shaft 3a has a diameter slightly smaller than that of the hole 42b. A preferable difference between the diameter in section of the end portion of the rotating shaft 3a and the diameter of the hole 42b is on the order of 30 to 50 .mu.m. Therefore, the eccentricity .DELTA.r is in the range of 15 to 25 .mu.m, and hence the tiny gap 6 varies by 30 to 50 .mu.m at portions (A) and (B) of the impeller 42 shown in FIG. 3.
In the thus constructed circumferential flow type fuel pump, the tiny gap 6 varies with rotation of the impeller 42. As a result, small variations (pulsation) are caused in the pressure of the fuel to be supplied to an engine or the like, or small vibrations are generated at the pump body 1, which vibrations become resonant with the fittings of the pump body 1 and the fuel supply piping, eventually leading to noise.